Effect of the pulse frequency on the structure, mechanical and tribological properties of Ti-Al-Ta-N coatings deposited by HiPIMS

Columnar microstructure significantly deteriorates performance of Ti-Al-Ta-N coatings obtained by physical vapor deposition. The present work is focused on studying the possibility to hinder the growth of columnar grains in the Ti-Al-Ta-N coatings using short-pulse high-power impulse magnetron sputtering (HiPIMS). The change of the pulse length is carried out by varying the pulse frequency f from 0.5 to 10 kHz at a constant duty cycle of 10 %. This results in decreasing the pulse length from 200 to 10 μs. It is found that the pulse frequency affects the parameters of magnetron discharge and ion flux at the substrate. Short-pulse HiPIMS realized at higher pulse frequencies (2–10 kHz) provides an increase in the ion flux arriving at the substrate compared to the HiPIMS processes at lower frequencies (0.5 and 1 kHz). The increased ion flux bombarding the growing coatings leads to evolution of their microstructure from the open columnar structure observed at f < 2 kHz to the dense microstructure containing only small columnar fragments at f ≥ 2 kHz. The microstructure modification provides improved mechanical properties and wear resistance of the Ti-Al-Ta-N coatings obtained at f ≥ 2 kHz. The maximum hardness and wear resistance were found in the coating deposited at 5 kHz.